Field of the Invention
This invention relates to a method for separating curds from whey and more specifically for cooling the curds while washing the whey therefrom during the production of cottage cheese.
In the commercial production of cottage cheese, skim milk usually at a temperature of 90.degree. is placed in a double walled vat typically having a depth of 39 to 40 inches and a capacity of 3500 gallons. One or more acidifiers or a culture is added to 90.degree. skim milk. Rennet may also be added to promote curd coagulation. When the curd has developed, stainless steel wires are run lengthwise, vertically and horizontally and then crosswise through the vat to cut the curd into 1/4 inch to 3/4 inch cubes. Then the curd is heated to further firm it and expell the whey, which is a waste product. The curd must then be separated from the whey, cooled and washed. In the prior art it is necessary to use a high volume of water to wash and cool the curd and remore the whey which, if not removed, taints the finished cottage cheese with an unpleasant acid taste.
In order to increase efficiency and reduce costs it is necessary to empty the vat as soon as possible after the curds have been cooked to make the vat available for a new batch. The cooked curds are cooled and washed outside of the vat. The cooked curds are, somewhat fragile and as they are cooled they become more fragile. The curds are susceptible of degrading into powder-like fines which then suspend in the liquid whey and flow away in the cooling and wash water. Such degrading reduces the amount of cottage cheese produced from a given volume of skim milk. While it is possible to filter out and collect these fines it is not practical to re-introduce them into the cottage cheese as the fines make the finished cottage product pasty and grainy in consistency which consumers do not like. Further, there is no economical way to agglomerate these fines back into the form of curds.
As the curds and whey exit the vat most of the whey is drained off and transfer water is added. To minimize degrading, in one prior art method of washing and cooling, the curds, residual whey and transfer water are pumped into a vertical washer and cooler tower. The curd remains generally stationary in a lower portion of the tower to avoid degrading it and the washing and cooling water flows upward through the stationary curd and out of the top of the tower. While such washer and coolers generally are satisfactory they have certain disadvantages including a slow cycling time and a requirement for a high volume of washing and cooling water. Even with a long period of washing and cooling, the whey may not be completely washed away and the curd sufficiently cooled because of bridging, and channeling which can occur as the cooling and wash water percolates upward through stationary curds in the tower. Such bridging results in hot spots of inadequately washed and cooled curd. An additional disadvantage of prior art apparatus and methods is that a high volume of washing and cooling water is required. Such wash and cooling water must be disposed of and sewage disposal costs are extraordinarily high and in some areas sewage districts refuse to accept such water and the processor must then arrange to have it trucked away.
The undesirably long time taken by prior art methods of washing and cooling the curd, the high sewage disposal costs incurred and the channeling have been tolerated because those skilled in the art believed that there was no practical apparatus or method that would permit the curds to mechanically agitated to accelerate cooling and make the wahing away of whey more efficient without incurring a cost prohibitive degradation of the curds.